The field of the invention pertains to large truck-trailers, in particular, to truck trailers having movable curtainsides wherein the entire sides of the trailer are of flexible material that can be drawn back to one end of the trailer to expose the entire cargo. Such trailers can be loaded much more quickly than trailers with rear doors. In some automotive related installations, the loading and unloading docks are equipped with fully automated loading and unloading equipment for curtainside trailers. An example of a curtainside trailer is disclosed in U.S. Pat. No. 4,828,316.
The roof of the truck trailer is supported by an upper rail on each side of the trailer. The upper rail extends the length of the trailer usually without support except at the ends of the trailer. In some trailers there may be removable or permanent intermediate supports for the rail. The upper rail also supports the curtain forming the curtainside and some additional vertical stress from the plurality of tie down straps that retain the curtain vertically taught.
The upper rail is commonly formed of an extruded structural aluminum, such as 6061-T6. The extruded shape provides a trolley-way for the curtain trolleys and a shelf or ledge to support roof bows. Grooves and flanges may also be provided for sealing gaskets and clip on gutters. The maximum allowable height of the truck trailer limits the height of the top of the upper rail measured from street level. The lower edge or bottom of the upper rail limits the vertical opening measured from the truck trailer bed or floor. Because of the dead weight, live weight, wind and snow loading and the vibration and torquing of the trailer in use, the upper rails are typically 5 inches or more in vertical depth for the standard curtainside 48 foot trailer. Any decrease in upper rail height results in an equal increase in vertical opening of the trailer and is a desirable goal, in particular, for truck trailers applied to automated loading and unloading systems. Applicants and their associates have previously developed 5 inch depth upper rails, however, further reduction in depth is a desirable goal. Nevertheless, despite the reduction in depth, the load carrying capacity and the limitations on maximum deflection must be met. With these generally conflicting requirements in view, applicants have invented the new upper rail disclosed below.